Machine tool

Abstract: A machine tool in which a tool or workpiece is mounted on a spindle (5) supported in anti-friction hydrostatic oil bearings (64, 65) lying in a closed-loop oil conduit including a reservoir (20). The spindle is driven by an electric motor (40) mounted at one end thereof. The motor has a liquid-cooled jacket (17) supplied in another closed-loop with liquid drawn from the same reservoir, so that the same liquid is used both to cool the motor and to lubricate the bearings.

Description: The present invention is directed to a machine tool in the form of a grinding machine for finishing camshafts, crankshafts, or similar workpieces. Grinding machine spindles have traditionally been driven by belts from induction motors or direct current (DC) motors. A major drawback utilising these prior art motors is the fact that belts must be used to rotate a grinding wheel and spindle. Belt forces imposed upon the spindle result in belt wear and contamination as well as velocity limitations, mechanical inefficiencies, as well as vibrations. Although these belt drives do benefit from low manufacturing costs and simple electrical control, these types of belt drives are detrimental, since they are noisy and wear out at speeds in excess of 3000 rpm. US-A-4180946 discloses a tool-holding spindle assembly, particularly for a grinding machine, comprising means for supporting the shaft of the spindle and a power drive, for example an electric motor for rotating the spindle. In accordance with the present invention there is provided a grinding machine comprising: a support body, a rotating elongated spindle, provided with a first end and a second end; first and second immovable bearings, each bearing encircling a portion of said first end or said second end of said elongated spindle, mounted in said support body; a rotating grinding wheel connected to said first end of said elongated spindle; a means for holding a workpiece proximate to said rotating grinding wheel; an electric motor affixed to said support body and cooperating with said elongate spindle to provide rotation thereto, said motor provided with a liquid cooling jacket for cooling said motor; and a liquid reservoir; characterized in that said machine further comprises: hydrostatic film bearings provided between said first and second immovable bearings and a portion of said first end and said second end of said elongated spindle; and a closed system including a plurality of feed lines for feeding liquid from said liquid reservoir to said hydrostatic film bearings and said liquid cooling jacket of said motor, said closed system further including return lines from said hydrostatic film bearings and said cooling jacket of said motor to said liquid reservoir; and wherein the same liquid is used both to cool the motor and to lubricate the bearings and protect said elongated spindle from wear. Hydrostatic film bearings are provided between the spindle and the wheelbase casing of the grinding machine. The same fluid used as the hydrostatic film bearing to remove heat from the rotating spindle is circulated through the motor cooling jacket. This helps to maintain a minimum temperature gradient throughout the mechanical system. If significant thermal differences existed between mechanism parts, bearing clearances could disappear or the wheelhead would distort. The present invention will now be described by way of example with reference to the accompanying drawings, wherein like reference characters indicate like or corresponding parts. In the draswings: Figure 1 is a sectional view of the motor-driven machine tool of this invention; Figure 2 is a side sectional view of the mechanism of Fig. 1 showing the mounting of the motor to the grinding spindle, and Figs. 1-3 illustrate the mechanical configuration of the grinding wheel and motor according to the present invention. The machine as shown in the drawings, is provided with a wheelbase and is supported by a base or a bed (not shown). A grinding wheel 18 is mounted on a rotary spindle 5 utilising a mounting flange 19. The grinding wheel is used to grind the outer of surfaces of workpieces 63, such as lobes, on crankshafts, camshafts, or similar devices. However, the tool could be utilised to grind the inner surfaces of various workpieces. These workpieces are supported by a support device 62 provided to move the grinding wheel, both up and down and front and back with respect to the workpiece 63. A frameless, rare-earth, permanent magnet motor 40 is mounted in a cantilever fashion on the spindle 5. The motor includes a rotor 13 and stator 14 which is provided in a motor frame 2 attached to the grinding machine mechanism utilising a plurality of screws 3. A circular end cap 9 is affixed to the motor frame 2 by a plurality of screws 8. The rotor 13 is axially clamped to the spindle 5 by a retainer clamp 11 having a shoulder 15. The spindle 5 is attached to this retainer clamp 11 by a plurality of screws 12. The spindle 5 also includes a shoulder 16, which with the assistance of the shoulder 15 applies the rotation of the rotor 13 to the spindle 5. A spacer 10 is provided between the retainer clamp 11 and one end of the spindle 5. Springs 66 provide a thrust loading between shoulders 67, 68, of the spindle 5. A stator sleeve 21 surrounds the outer periphery of the motor and is provided with a labyrinth 17 through which fluid, such as oil, flows to cool the motor. This oil flow is pumped through pump 29 powered by a motor 27 from an oil reservoir 20 through line 24 to the labyrinth 17. This oil, now at an elevated temperature, flows out from the labyrinth 17 through a line 25 to a heat exchanger 30 that reduces the temperature of the oil. Shown in Fig. 1, fluid lines 31 and 32 used to direct fluid such as water to and from the heat exchanger 30 for cooling the oil. However, the exact type of heat exchanger utilised is not important, and virtually any cooling medium and heat exchanger can be employed. Hydrostatic fluid film bearings 41, 42 are provided between the spindle 5 and two immobile bronze bearings 64, 65. Each of the bearings is provided with four pockets, which encircle the wheel spindle. One of the bearings is provided close to the anterior end of the spindle 5 near the grinding wheel mounting flange 19, and the second bearing is provided near the posterior end of the spindle near the motor 40. These bearings consist of oil and are supplied by the same oil reservoir 20 that supplies oil to the cooling jacket labyrinth 17. Motor 27 powers a pump 28 for pumping the oil through lines 22 and 23 to the bearings 41, 42. Oil will then flow through a drain cavity 4 provided in the wheelbase casing. This oil will then flow through drain line 26 and back to the oil reservoir 20. Because the same oil is supplied from reservoir 20 to both the labyrinth 17 and the hydrostatic bearings 41, 42, only a single heat exchanger 30 need be utilised. This particular configuration would maintain the oil at a temperature between ambient and approximately 150°F (66°C). Additionally, the type of oil which is employed is not crucial to the present invention. One such oil that can be employed is Mobil DTE11 spindle oil. It will thus be seen that this invention provides a machine tool which uses the same liquid as both a lubricant and a coolant.

Claims: A grinding machine comprising: a support body (1); a rotating elongated spindle, provided with a first end and a second end; first and second immovable bearings (64,65), each bearing encircling a portion of said first end or said second end of said elongated spindle, mounted in said support body; a rotating grinding wheel (18) connected to said first end of said elongated spindle; a means for holding a workpiece proximate to said rotating grinding wheel; an electric motor (40) affixed to said support body and cooperating with said elongate spindle to provide rotation thereto, said motor provided with a liquid cooling jacket for cooling said motor; and a liquid reservoir (20); characterized in that said machine further comprises: hydrostatic film bearings (41,42) provided between said first and second immovable bearings and a portion of said first end and said second end of said elongated spindle; and a closed system including a plurality of feed lines for feeding liquid from said liquid reservoir to said hydrostatic film bearings and said liquid cooling jacket of said motor, said closed system further including return lines from said hydrostatic film bearings and said cooling jacket of said motor to said liquid reservoir; and wherein the same liquid is used both to cool the motor and to lubricate the bearings and protect said elongated spindle from wear. A grinding machine as claimed in claim 1, in which each closed system includes a conduit (22, 24) connected to the outlet of a pump (28, 29) that draws liquid from the reservoir, the pumps preferably being driven by a common motor (27). A machine as claimed in claim 1 or 2, in which one of the closed systems includes a fluid-cooled heat exchanger (30). A machine as claimed in claim 3, in which the heat exchanger is located in the liquid-return conduit (25) from the motor (40) driving the spindle (5), and in which the heat exchanger is adapted to be cooled by water. A machine as claimed in any preceding claim, in which the liquid in the reservoir is an oil. A machine as claimed in any preceding claim, in which the liquid-cooled jacket of the motor (40) comprises a stator having in it a labyrinthine passage (17) traversed by the coolant liquid.

Inventors: HYKES TIMOTHY W, PFLAGER WILLIAM W, HYKES,TIMOTHY W, PFLAGER,WILLIAM W
Applicants: WESTERN ATLAS INT INC, WESTERN ATLAS INC.
Application year: 1994
Main classification: B24B41
IPC codes: H02K9, H02K5, B23Q1, B24B41